Absolute include paths are silently ignored

[UebelAndre]

Passing includes = ["/some/path"] results in this value getting ignored. I think the cause is from:

rules_cc/cc/common/cc_helper.bzl

Lines 798 to 799 in 31ddd5f

	if includes_attr.startswith("/"):
	continue

Instead, this should warn users or throw an error explaining that the target is misconfigured.

[pzembrod]

Rejecting absolute include paths is generally intended as we want builds to be hermetic.
However, silently ignoring them is obviously not the best behaviour.
We should throw a build error in this case that guides the user to remove the absolute include path from the broken target if a target gets broken by this.
It needs to be added to the release notes.